HCV is a single stranded, positive-sense RNA virus, with a genome of around 9,600 bases belonging to the Flaviviridae family of viruses in the hepacivirus genus. The NS5B region of the RNA polygene encodes a 65 kDa RNA dependent RNA polymerase (RdRp), which is essential to viral replication. Following the initial acute infection, a majority of infected individuals develop chronic hepatitis because HCV replicates preferentially in hepatocytes but is not directly cytopathic. In particular, the lack of a vigorous T-lymphocyte response and the high propensity of the virus to mutate appear to promote a high rate of chronic infection. Chronic hepatitis can progress to liver fibrosis, leading to cirrhosis, end-stage liver disease, and HCC (hepatocellular carcinoma), making it the leading cause of liver transplantations.
There are six major HCV genotypes and more than 50 subtypes, which are differently distributed geographically. HCV genotype 1 is the predominant genotype in Europe and the US. The extensive genetic heterogeneity of HCV has important diagnostic and clinical implications, perhaps explaining difficulties in vaccine development and the lack of response to current therapy.
Transmission of HCV can occur through contact with contaminated blood or blood products, for example following blood transfusion or intravenous drug use. The introduction of diagnostic tests used in blood screening has led to a downward trend in post-transfusion HCV incidence. However, given the slow progression to the end-stage liver disease, the existing infections will continue to present a serious medical and economic burden for decades.
Current HCV therapies are based on (pegylated) interferon-alpha (IFN-α) in combination with ribavirin. This combination therapy yields a sustained virologic response in more than 40% of patients infected by genotype 1 viruses and about 80% of those infected by genotypes 2 and 3. Beside the limited efficacy on HCV genotype 1, this combination therapy has significant side effects and is poorly tolerated in many patients. Major side effects include influenza-like symptoms, hematologic abnormalities, and neuropsychiatric symptoms. Hence there is a need for more effective, convenient and better-tolerated treatments.
Experience with HIV drugs, in particular with HIV protease inhibitors, has taught that sub-optimal pharmacokinetics and complex dosing regimens quickly result in inadvertent compliance failures. This in turn means that the 24 hour trough concentration (minimum plasma concentration) for the respective drugs in an HIV regime frequently falls below the IC90 or ED90 threshold for large parts of the day. It is considered that a 24 hour trough level of at least the IC50, and more realistically, the IC90 or ED90, is essential to slow down the development of drug escape mutants. Achieving the necessary pharmacokinetics and drug metabolism to allow such trough levels provides a stringent challenge to drug design.
The NS5B RNA-dependent RNA polymerase (RdRp) is absolutely essential for replication of the single-stranded, positive sense, RNA genome. This enzyme has elicited significant interest among medicinal chemists. Both nucleoside and non-nucleoside inhibitors of NS5B are known.
Nucleoside inhibitors can act either as a chain terminator or as a competitive inhibitor, which interferes with nucleotide binding to the polymerase. To function as a chain terminator the nucleoside analog must be taken up by the cell and converted in vivo to a triphosphate to compete for the polymerase nucleotide binding site. This conversion to the triphosphate is commonly mediated by cellular kinases which imparts additional structural requirements on a potential nucleoside polymerase inhibitor. In addition this limits the direct evaluation of nucleosides as inhibitors of HCV replication to cell-based assays capable of in situ phosphorylation.
Several research groups have attempted to develop nucleosides as inhibitors of HCV polymerase, but while a handful of compounds have entered clinical development, none have proceeded all the way to registration. Amongst the problems that HCV targeted nucleosides to date have encountered are toxicity, mutagenicity, lack of selectivity, poor efficacy, poor bioavailability, sub-optimal dosage regimes, and ensuing high pill burden and cost of goods.
Several patents and patent applications as well as scientific publications disclose nucleoside analogs having HCV inhibitory activity. WO 2007/020193 discloses phosphoramidate derivatives of certain nucleosides. WO 2008/043704 discloses 4-amino-1-((2R,3 S,4S,5R)-5-azido-4-hydroxy-5-hydroxymethyl-3-methyl-tetrahydro-furan-2-yl)-1H-pyrimidin-2-one and ester derivatives as HCV polymerase inhibitors. WO 2009/067409 discloses 2′,4′-substituted nucleosides as antiviral agents.
There is a need for HCV inhibitors that may overcome the disadvantages of current HCV therapy such as side effects, limited efficacy, the emerging of resistance, and compliance failures, as well as improve the sustained viral response.
The present invention concerns phosphoramidate derivatives of 1-((2R,3S,4S,5R)-5-azido-4-hydroxy-5-hydroxymethyl-3-methyl-tetrahydrofuran-2-yl)-1H-pyrimidin-2,4-di-one that are HCV inhibitors with useful properties as regards one or more of the parameters: antiviral efficacy, favorable profile of resistance development, lack of toxicity and genotoxicity, favorable pharmacokinetics and pharmacodynamics, such as an increased concentration of the mono or triphosphate analogs in the liver, increased absorption, in particular adsorption by liver cells, and ease of formulation and administration.